7.11 Perform voltage calibration with the BQ34Z100-G1

[MUSIC PLAYING] Today, we will take a look at performing voltage calibration with the BQ34Z100-G1 multi-chemistry multi-cell battery gauge. This video is part of a series focused on the configuration and calibration of the BQ34Z100-G1 device. We will learn how to configure the parameters involved in voltage calibration and walk through voltage calibration with the recommended toolchain. On our computer, we will be using Battery Management Studio, also known as bqStudio. It is the graphical user interface portion of the toolchain that allows us to program, configure, and log the battery gauge.
We will use an EV2400 to facilitate communication between bqStudio on the computer and the battery gauge. The EV2400 is powered from the USB bus. We will also be using an evaluation module, the BQ34Z100EVM. This evaluation module includes the battery gauge, connectors for I2C and HDQ communication, jumpers for hardware configuration, and more. This video assumes that your toolchain is installed, updated, and configured as shown in the BQ34Z100-G1 out-of-box Quickstart Guide. Click on the Quickstart Guide link for step-by-step instructions. For more information on the device, click on the Product Folder link for access to technical documents, tools, software, firmware, support, and training.
In addition to the toolchain, test equipment is also required. A regulated power supply will be used to power the device and also to simulate the battery. A multimeter will be used to measure the voltage of the power supply at the terminals of the evaluation module.
Let's set up our device. Connect the keyed four-wire cable to Port 2, the I2C connector on the EV2400, and to J7, the I2C connector on the evaluation module. Connect the USB cable to the EV2400 and the computer. Connect your power supply to the BAT plus and BAT minus terminals on the evaluation module. Slowly increase the voltage supply to the operational voltage your board is configured to support. Since I am following the settings of the Quickstart Guide, my voltage is now set to four volts.
And lastly, launch bqStudio. With the BQ34Z100-G1 dashboard loaded, move your cursor to the ribbon and select Data Memory to open the Data Memory window. In the Data Memory window, select Calibration to view calibration parameters. Our parameter of interest is voltage divider, which is set at 5,000 millivolts. In the Dashboard window, the reported voltage of the gauge is 4,041 millivolts.
The voltage divider is simply the ratio of the voltage divider in millivolts. The internal voltage divider has a ratio of 5:1. For every 5,000 millivolts applied to the device, 1,000 millivolts is sensed by the ADC. We calibrate the voltage for the device by increasing or decreasing the voltage divider ratio until the reported voltage matches the actual voltage.
For example, with the voltage divider set to 10,000 millivolts, the reported voltage is 8,082 millivolts. Decreasing the voltage of the voltage divider to 5,000 millivolts results in a decrease of voltage reported by the gauge from 8,082 millivolts to 4,041 millivolts. In this example, the internal voltage divider that supports up to five volts has a ratio of 5,000 to 1,000. For reference, here are the approximate ratios for the external divider on the evaluation module.
Although we can now manually modify the voltage divider value in bqStudio by trial and error, we can instead use the Calibration tool in bqStudio to modify the voltage divider parameter. Here are the steps we will follow for calibration. When calibrating the voltage, it is recommended to use the nominal voltage of the battery stack. In this example, we're using four volts. Your voltage may vary.
Now let's calibrate. In the ribbon, click on Calibration to open the Calibration window. In the Calibration window, ensure that all checkboxes are de-selected. Select the Calibrate Voltage checkbox.
With the multimeter, measure the applied voltage from the BAT plus to the BAT minus terminal on the evaluation module. Input the measured applied voltage to the Applied Voltage field, in millivolts. Click on the Calibrate Gas Gauge button to calibrate the gas gauge. A green checkmark will indicate that calibration was successful and that the voltage divider parameter has been successfully updated. We now know about the parameters involved in voltage calibration and have performed a successful voltage calibration of the BQ34Z100 battery gauge.